§ 8 Permanent counter.
In the passports for electric meters such a parameter is indicated as the counter constant. This paragraph tells what it is and why it is needed.
It was said above that the moment of rotation of the counter disk is proportional to the load, i.e.
and the opposing moment is proportional to the frequency of rotation of the disk, i.e.
If the disk rotates for t units of time, then at equilibrium (i.e. at steady-state rotation frequency) we will have.
and since Pt = A and nt = N , then
where N is the number of revolutions of the disk corresponding to the energy A; C - counter constant.
From the last expression it can be seen that the amount of energy measured by the counter is proportional to the number of disk revolutions.
The disk with the help of a worm pair is connected with a counting mechanism, which determines the amount of electricity.
In contrast to the pointer pointing devices, in which the measured value is determined by the reading of the arrow, when measuring energy by the meter, it is necessary to make two readings: A1 at time t1 and A2 at time t2.
Then the measured amount of energy A with the time interval t = t2-t1 is determined as the difference between the two readings, i.e.
A = A2-A1
The constant of the counter is determined from the expression
C = A / N.
The constant shows the number of units of electricity per unit disk revolution.
It should be borne in mind that the nominal constant of the counter C nom is determined by the readings of the counting mechanism for one revolution of the disk and is constant.
The actual constant of counter C is determined by the actual amount of energy counted by the counter for one revolution of the disk.
Then the error of the counter can be expressed:
The number of revolutions of the disk for which the readings of the counting mechanism change by a unit of the measured value, for example, by 1 kWh, is called the gear ratio of the counter.
This counter parameter is also a constant purely mechanical quantity and is associated with the gear ratio of the counting mechanism.
The counter constant and the gear ratio of the counter are interrelated. It is customary to determine the counter constant as the number of watt-seconds per disk revolution. If the gear ratio is N A obor / kWh, then
The gear ratio of the counter is usually indicated on the counter: 1 kW * h = N A disk speed. For example, if 1 kWh is indicated on the dashboard = 1250 disk revolutions, then the counter constant will be equal to:
At nominal load, the disc rotates at a certain frequency, called nominal. This parameter is sometimes indicated in the technical specification of the counter (rounded rpm). The nominal rotational speed indirectly characterizes the wear resistance of the disk supports of the meter: the smaller it is, the more durable the supports are.